India's PFBR Achieves Criticality Milestone

India's Prototype Fast Breeder Reactor at Kalpakkam, Tamil Nadu, attained criticality on April 6, 2026, marking a significant milestone in the country's nuclear energy program. Prime Minister Narendra Modi announced the achievement, describing it as a defining step in India's civil nuclear journey and the start of the second stage of its three-phase nuclear initiative.

The 500 megawatt electric reactor, designed and built indigenously by the Indira Gandhi Centre for Atomic Research and Bharatiya Nabhikiya Vidyut Nigam Limited, uses uranium-plutonium mixed oxide fuel and liquid sodium as a coolant. Criticality refers to the point at which the reactor sustains a controlled nuclear chain reaction, producing enough neutrons to maintain fission without external input. This process allows the reactor to generate more fissile material than it consumes by converting surrounding uranium-238 into plutonium, a key feature of fast breeder technology.

Officials noted that the project, which began construction in 2004, faced delays and cost overruns but overcame technical challenges, including adaptations to the fuel handling system. Fuel loading started in October 2025, followed by low-power...